The present invention relates, in general, to semiconductor devices and, more particularly, to semiconductor sensing devices.
Acceleration sensors are used in motion sensing applications such as, for example, motion sensing for controlling air bags in automobiles. One type of acceleration sensor includes a field effect transistor having a movable gate structure. When the substrate on which the field effect transistor is fabricated experiences an acceleration in a normal direction perpendicular to the front surface of the substrate, the movable gate moves towards or away from the front surface of the substrate. A current flowing in the field effect transistor changes in response to the motion of the movable gate in the normal direction. An amplifier coupled to the field effect transistor amplifies the current change and senses the normal acceleration.
To sense an acceleration in a lateral direction substantially parallel to the front surface of the substrate, a field effect transistor is fabricated to have a movable gate that is movable in the lateral direction. When the substrate experiences a lateral acceleration, the motion of the movable gate changes the channel width of the field effect transistor, thereby modulating the current carrying capability of the field effect transistor. An amplifier coupled to the field effect transistor amplifies the current change in the field effect transistor and senses the lateral acceleration. However, the change in the channel width is usually very small compared with the channel width of the field effect transistor. Therefore, the sensitivity of the field effect transistor to the lateral acceleration is low, usually at least ten time lower than the sensitivity of a field effect transistor of comparable size to the normal acceleration.
Accordingly, it would be advantageous to have a semiconductor sensing device and a method for fabricating the semiconductor sensing device. It is desirable for the sensing device to be able to accurately sense a lateral acceleration. It is also desirable for the method for fabricating the sensing device to be cost efficient and compatible with standard Metal Oxide Semiconductor (MOS) technologies. It would be of further advantage if the sensing device is simple, reliable, and can be easily implemented with other integrated circuit devices in a monolithic semiconductor chip.